Often it is necessary to have someone working on a rig platform (such as a derrick tubing board, for example). Sometimes, however, rig workers on such platforms are faced with a blowout or fire or some other kind of accident and need to escape quickly from the platform in order to avoid being seriously or fatally injured. Various t-bar or chair-based systems exist for providing a means for escaping from such platforms; however a difficulty encountered with known escape systems is that functionally impaired workers (e.g. workers who are in a state of shock as a result of the accident, or workers who have been burned, or disoriented by gases as a result of the accident) can have difficulties in accessing and operating them.
In Canadian Patent Application no. 2,539,883 filed Mar. 16, 2006 by Boscher et al and entitled APPARATUS FOR ESCAPING AREA OF ACCIDENT, which is incorporated by reference in its entirety herein, an apparatus is provided for emergency escape from a drilling rig platform along a path defined by at least one cable extending between the platform and a remote, terminal location. The apparatus includes a frame in which a top of the frame is located above a bottom of the frame when the frame is erect. The frame defines an interior space large enough to accommodate a worker. A locking system includes a locking mechanism and also a foot-actuated disengager that is located at least proximate to the bottom of the frame. The locking mechanism is adapted to interlock with a mating portion on the platform to prevent the frame from traveling away from the platform when the locking mechanism engages the mating portion. The disengager is connected to the locking mechanism and has a foot receiving surface region upon which force can be applied to displace the disengager between a first, engaged position and a second position to disengage the locking mechanism from the mating portion. The frame will travel away from the platform to the terminal location under gravity when the locking mechanism is disengaged.
The Boscher et al. device uses an automatic braking system attached at the bottom of the frame, beneath the disengager to permit quick descent along the path defined by the cable, but still sufficiently slowed down to prevent an excessively forceful impact when the frame arrives at the terminal location.
Conventional systems include braking systems that employ hand actuated levers (including overriding automatic brake settings). A preferred system disclosed in the Boscher et al device is the Rollgliss® Rescue Emergency Descent Device friction brake, model no. 3303001 manufactured by DBI/SALA & Protecta. This system employs a series of brake pads that expand into a brake drum during descent to slow descent to a rate of about 15 feet/second.
Because of the intangible factors that will affect braking power with such systems, the rate at which enclosures equipped with such systems will fail will invariably have considerable variability, which makes it difficult to ensure compliance with applicable safety standards, such as those mandated by the Canadian Association of Oilwell Drilling Contractors (CAODC). Such standards mandate, amongst other things, that the enclosure land with a speed no greater than 12 ft/s.
The release of the pod pulls on the spooled cable, causing the pads to be placed in frictional contact with a drum to slow the descent of the pod. The physical contact between the pads and the drum creates a potentially hazardous risk of overheating of the components and cable and causes wear on both items which must be taken into account in maintenance operations, especially given that the device is hopefully only sporadically used. Additionally, both the pads and the drum should be subjected to regular maintenance and/or inspections to ensure that corrosion does not build up on either surface which may deleteriously impact the gripping performance of the braking system. Indeed, such braking systems face recertification inspections after use and on a semi-annual or annual basis.
Moreover, such braking systems have a latch mechanism that call for manual engagement of a spooled cable clasp when the enclosure was brought to the side of the derrick or structure. Such manual engagement necessarily incurs a risk of human error, which, in the frenetic occasions when the pod is to be used, could have catastrophic consequences.